Olefin polymerization, particularly the polymerization of propylene with TiCl.sub.3 catalysts, is a highly developed technology. Various catalysts and processes to produce such catalysts have been developed for the production of highly stereospecific polyolefins. High productivity and low solubles content are two goals that frequently were mutually exclusive. Commercial unmodified TiCl.sub.3 catalysts for propylene polymerization generally permit productivities of around 600-2000 pounds of polypropylene per pound of catalyst, with xylene-solubles of about 8-15 weight percent. Modern high productivity TiCl.sub.3 propylene polymerization catalysts are those with productivities around 3000-4000 pounds of polymer per pound of catalyst with xylene-solubles content of about 5-15 weight percent.
Specific procedures and additives have been developed to increase productivity and reduce xylene-solubles content. A problem of such additives is, however, that they frequently are contained in small quantities in the final polymer and render the final polymer useless for certain food related applications.